1. Field of the Invention
The present invention relates to welding equipment, and more particularly to spot welding equipment used for welding car bodies.
2. Description of the Related Art
The bodies of automobiles comprise plate-like metal members which are generally welded by multi-spot welding using a welding jig. A robot mechanism may also be included in the welding process so that several portions can be welded at the same time to improve work efficiency. In this sort of welding equipment, as schematically shown in FIG. 8, when a car body 2 is conveyed to a welding position by a conveying means (not shown in the drawing), welding equipment, generally referred to by 47, having receiving stanchions 8 and a back electrode 42 formed on a mount 46, approaches a welding position 10. Electrode tips 27 formed on the back electrode 42 are then brought into contact with the car body 2. Upper electrodes 43 having electrode tips 28 move downward and are positioned opposite the electrode tips 27 of the back electrode 42 in the welding position 10. Car body 2 is then spot welded at the positions corresponding to oppositely facing electrode tips 27 and 28 by charging the electrode tips with electricity.
When welding a channel-like portion of a car body wherein the channel has portions of differing depths or widths, such as the portion 44 in FIG. 8, it is necessary to move the car body 2 to a second welding position to weld different portions of the car body. Thus, an intervening step of moving the car body to the electrodes is required before performing the second weld. This intervening step reduces the efficiency and cost-effectiveness of the welding process and the assembly line.
Conventional welding equipment as described above cannot perform welding at different positions in the same processing step when respective welding positions of the car body have similar form but different dimensions. Thus, an additional step in which the car body is moved to a second weld position becomes necessary. In other words, it is necessary to conduct separate steps equivalent in number to the total number of types and configuration of car bodies being welded or the number of welding positions on a car body.